This invention relates to an exhaust gas purifying device for a watercraft propulsion unit and, more particularly, to an improved catalytic gas exhaust treatment arrangement for an engine associated with such a unit.
It is well known that exhaust gases from an internal combustion engine may be treated by a system that includes a catalyst that will cause a chemical reaction to occur that renders certain of the exhaust gas constituents harmless. In connection with such arrangements, it is conventional to position the catalyst in such a manner that it is contained within the exhaust system or an exhaust passage of the engine.
The treatment of the exhaust gases from an internal combustion engine is particularly important with outboard motors. As is well known, such outboard motors oftentimes discharge their exhaust gases into the atmosphere back through the body of water in which the outboard motor is operating. As such, it is particularly important to remove from the exhaust gases materials which would pollute the water in which the watercraft is operating.
In outboard motors, like many other applications, it is desirable to insure good contact between the exhaust gases and the catalyst in order to insure effective treatment before discharge to the atmosphere. Also, it is desirable to insure that the catalyst operates at the necessary temperature so as to achieve the desired exhaust gas treatment. In an effort to attain, and maintain, a high enough temperature so that the catalyst may perform its intended functions effectively, the catalyst is sometimes placed close to exhaust output ports which lead directly from the engine's combustion chambers. A suitable operating temperature for the catalyst is likely to be found at such a location since the hot exhaust gases will help to provide the desired high temperature.
The problem of treating the exhaust gases in an outboard motor is particularly acute. One of the main reasons for this is due to the extremely compact nature of an outboard motor. It is, of course, desirable to achieve a good and complete catalytic treatment of the exhaust gases, while maintaining a compact structure for an outboard motor.
Unfortunately, the prior emission control arrangements which employ a catalyst contained within an exhaust passage, as set forth above, may not permit the realization of all of the above-discussed desirable objectives under all engine operating conditions.
Such known catalytic devices are often in direct contact with certain other engine parts. Under low load engine operating conditions a portion of the heat generated as a result of the emission control catalytic reactions is, thus, transferred from the reaction sites to these other engine parts. Accordingly, it is difficult to raise the temperature at the reaction sites to the necessary temperature for activating the catalyst, and to maintain this temperature during low load engine operation, as the heat is traveling away from the catalyst and on to the associated engine parts. Consequently, it is difficult to effectively treat exhaust gases under low load conditions. This is especially true in a structure wherein the catalyst is placed proximate to the exhaust ports leading from the combustion chambers as the amount of heat imparted to the catalyst will be particularly high and, thus, the amount of heat transferring away from the catalytic reaction sites will be high.
Furthermore, under high load engine operating conditions, the transfer of heat from the reaction sites to the other engine parts makes the engine susceptible to overheating. Of course, where the catalyst is placed proximate the combustion chamber exhaust ports, and therefore incurs a particularly high degree of heat, such problem is particularly troublesome. The susceptibility of the engine to readily overheat during high load engine operation necessitates the utilization of a larger sized water pump in combination with the engine, than otherwise would be required, in order to prevent engine overheating. Accordingly, the overall size of the engine encasement assembly must be increased somewhat to accommodate the engine and large water pump, and the degree of design freedom for placement of the engine parts is decreased.
It is, therefore, a principal object of this invention to provide an improved arrangement for treating the exhaust gases in an internal combustion engine with a catalyzer.
It is a further object of this invention to provide an exhaust emission control arrangement, having a catalyst disposed in an engine exhaust passage, which permits good contact of engine exhaust gases with the catalyst and which allows the ready attainment, and maintenance, of the temperature of catalyst activation.
It is still a further object of this invention to provide an exhaust emission control arrangement, having a catalyst disposed in an engine exhaust passage, which is compact in size, yet which provides a high degree of design freedom for placement of the various engine parts within an encasement assembly.